An oil or fat is essential as a nutrient and energy source for a body (primary function), and moreover, is important for providing the so-called sensory function (secondary function), which satisfies preference such as a taste and an aroma. In addition, an oil or fat containing diacylglycerols at a high concentration is known to have a physiological action (tertiary function) such as a body fat-burning action.
An untreated oil or fat obtained by squeezing seeds, germs, pulp or the like of a plant contains, for example, fatty acids, monoacylglycerols, odor components or the like. Further, when an oil or fat is subjected to a heating process by using a transesterification reaction, an esterification reaction, hydrogenation treatment or the like, trace components are produced in the oil or fat, and thus the taste and flavor of the oil or fat is impaired. In order to use such oil or fat as edible oil, the taste and flavor thereof needs to be improved by removing these trace components. The so-called deodorization treatment in which an oil or fat is brought into contact with water vapor at high temperature under reduced pressure is generally carried out as means for removing the trace components (Patent Document 1).